PHILADELPHIA, PA—Morbidly obese patients may require a lower mg/kg/day vancomycin dose than obese patients to reach the desired trough of >15-20mg/L, according to data presented at 2014 IDWeek.

Haley Morrill, PharmD, of the College of Pharmacy, University of Rhode Island, Kingston, presented findings of a retrospective cohort study that included obese patients (BMI ≥30) admitted to VA hospitals with Methicillin-resistant S. aureus (MRSA)-positive cultures. Patients initiating vancomycin in the hospital were selected for inclusion. 

The researchers identified 263 obese and 73 morbidly obese patients treated with vancomycin with appropriately collected vancomycin trough levels.  Total body weight ranged from 69–244kg. The mean total daily dose of vancomycin was lower in obese vs. morbidly obese patients (2005±736 vs. 2298±923mg, P<0.05). However, the mean mg/kg/day dose was higher in obese vs. morbidly obese patients (20±7 vs.17±7mg/kg/day, P<0.05). 

About 20% of patients in each group had a vancomycin trough level of >15–20mg/L.  The mean mg/kg/day vancomycin dose was also higher in obese vs. morbidly obese patients with a trough of >15–20mg/L (20±7 vs. 15±7mg/kg/day, P<0.05).

In obese patients, the standard dose of ~30mg/kg/day was appropriate for reaching a vancomycin trough of >15–20mg/L (odds ratio [OR] 3.348, 95% confidence interval [CI] 1.2–9.2).  In morbidly obese patients, as the mg/kg/day vancomycin dose increased, the odds of achieving a vancomycin trough of 15–20mg/L decreased (OR 0.870, 95% CI 0.78–0.98).

“Despite the increasing burden of obesity, the optimal dose of vancomycin in obese and morbidly obese patients with MRSA pneumonia has been largely unknown,” Dr. Morrill stated. The current study adds to the knowledge of vancomycin administration in this population. However, “further research is warranted to determine which vancomycin trough levels are associated with the best outcomes in obese and morbidly obese patients,” Dr. Morrill added.